Modified resin systems suitable for liquid resin infusion

ABSTRACT

A curable composition for liquid resin infusion (LRI) and a manufacturing process for producing a molded article. The curable composition includes:
         a) no more than 5.0 wt % of a thermoplastic polymer;   b) no more than 5.0 wt % of nano-sized core-shell particles;   c) no more than 5.0 wt % of nano-sized inorganic particles;   d) an epoxy resin component; and   e) one or more amine curing agent(s),
 
wherein the initial viscosity of said curable composition is no more than 5 Poise at a temperature within the temperature range of from about 80′ C. to about 130′ C.

This application claims the benefit of United Kingdom Application No.1422564.3 filed on Dec. 18, 2014, the disclosure of which isincorporated herein in its entirety.

The present disclosure relates to modified resin systems suitable forliquid resin infusion applications. The present disclosure furtherrelates to processes for the preparation of a composite material derivedfrom the modified resins, and applications thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the morphology a cured resin, in which inorganic particles(4) surrounds the outer surface of a phase separated thermoplasticdomain (2).

FIG. 2 shows the morphology of a cured resin which is similar to thatshown in FIG. 1 but does not contain nano-silica particles.

FIG. 3 shows the viscosity as a function of temperature for fourdifferent resin formulations.

DETAILED DESCRIPTION

Liquid resin infusion (LRI) is a process used to manufacturefiber-reinforced composite structures and components for use in a rangeof different industries including the aerospace, transport, electronics,and building and leisure industries. The general concept in LRItechnology involves infusing resins into a fiber reinforcement, fabricor a pre-shaped fibrous reinforcement (“preform”) by placing thematerial or preform into a mold (two-component mold or single-sidedmold) and then injecting resin under high pressure (or ambient pressure)into the mold cavity or vacuum bag sealed single-sided mold. The resininfuses into the material or preform resulting in a fiber-reinforcedcomposite structure. LRI technology is especially useful inmanufacturing complex-shaped structures which are otherwise difficult tomanufacture using conventional technologies. Variation of liquid resininfusion processes include, but are not limited to, Resin Infusion withFlexible Tooling (RIFT), Constant Pressure Infusion (CPI), Bull-ResinInfusion (BRI), Controlled Atmospheric Pressure Resin Infusion (CAPRI),Resin Transfer Molding (RTM), Seemann Composites Resin Infusion MoldingProcess (SCRIMP), Vacuum-assisted Resin Infusion (VARI) andVacuum-assisted Resin Transfer Molding (VARTM).

In prepreg resin formulations, high levels of toughness are gene allyachieved through the addition of about 10 to 30 wt % of a thermoplastictoughener to the base resin. However, addition of such tougheners to LRIsystems generally results in an unacceptable increase in the viscosityof the resin. In the specific case of particulate toughener, there maybe additional filtering issues in the textile. These limitations renderthe addition of tougheners conventionally added in prepreg formulationsgenerally unsuitable in conventional LRI applications where the balanceof final part toughness and process viscosity of the LRI formulation arekey technology drivers,

One technology to toughen fiber-reinforced composite structuresmanufactured by LRI technologies is to integrate the toughener into thepreform itself. For example, a soluble toughening fiber may be directlywoven into the preform thereby eliminating the need to add toughenerinto the resin which otherwise would increase the viscosity of the resin(rendering it unsuitable for resin infusion). Another example is the useof soluble or insoluble veils comprising of toughener used as aninterleaf with the reinforcement of the preform. However, in either ofthese methods, the manufacturing process may be more complicated andcostly, in addition to increasing the risk of hot/wet performanceknock-downs and solvent sensitivity with a polymer based insolubleinterleaf.

Another technology is the addition of particles to the resin. The amountof particles required to reach a suitable toughness threshold, however,is often high resulting in a viscous resin requiring a very narrowprocess window that is generally unfavorable for LRI. WO-2011/077094-A1addresses these issues by providing a curable modified resin formulationcomprising core-shell rubber particles or hollow particles in a carrierresin and further comprising a thermoplastic toughening agent, such thatwhen cured the particles are uniformly dispersed throughout the resin.

However, it remains desirable to further improve the CompressionStrength After Impact (CSAI), which measures the ability of a compositematerial to tolerate damage, while maintaining excellent hot-wetcompressive performance (hot-wet open-hole compression (H/W-OHC)strength), which measures the way in which the open-hole compression(OHC) strength decreases at elevated temperatures after a prolongedexposure to moisture. The OHC strength of conventional composites istypically fairly constant below room temperature (for instance from roomtemperature (21° C.) down to about −55° C.) but can deterioratesignificantly at elevated temperatures (for instance 70° C.) whensaturated with moisture There also remains a need to further improve theprocessability of the curable composition in LRI processes, i,e. thatthe initial viscosity of the injected composition should be low andpreferably also that the viscosity remains stable over time at anelevated processing temperature, thereby ensuring that the “pot-life” ismaintained or extended.

It is therefore an object of this disclosure to provide a resin systemwhich provides improved CSAI, and which exhibits excellent H/W OHC,preferably without detriment to processability and preferably withimproved processability. It is a further object of this disclosure toprovide a resin system which provides improved CSAI and which exhibitsexcellent H/W-OHC, preferably without detriment to processability andpreferably with improved processability. It is a further object of thisdisclosure to provide a resin system with improved processabilitywithout detriment to CSAI and/or H/W-OHC and preferably with improvedCSAI while retaining excellent H/W-OHC.

According to a first aspect of the present disclosure there is provideda liquid resin infusion (LRI) manufacturing process for producing amolded article, comprising the steps of providing a curable composition,injecting said curable composition into the mold, and curing saidcurable composition, wherein the curable composition comprises, consistsessentially of, or consists of:

-   -   a) no more than 5.0 wt % of a thermoplastic polymer;    -   b) no more than 5.0 wt % of core-shell particles wherein said        core-shell particles have a particle size in the range of from        about 50 nm to about 800 nm;    -   c) no more than 5.0 wt % of inorganic particles wherein said        inorganic particles have a particle size in the range of from        about 2.0 nm to about 800 nm;    -   d) an epoxy resin component which is or comprises one or more        epoxy re in precursor(s); and    -   e) one or more amine curing agent(s),        wherein the initial viscosity of said curable composition is no        more than 5 Poise at a temperature within the temperature range        of from about 80′ C. to about 130″ C.

According to a second aspect of the present disclosure there is provideda curable composition which comprises, consists essentially of, orconsists of:

-   -   a) no more than 5.0 wt % of a thermoplastic polymer;    -   b) no more than 5.0 wt % of core-shell particles wherein said        core-shell particles have a particle size in the range of from        about 50 nm to about 800 nm;    -   c) no more than 5.0 wt % of inorganic particles wherein said        inorganic particles have a particle size in the range of from        about 2.0 nm to about 800 nm;    -   d) an epoxy resin component which is or comprises one or more        epoxy resin precursor(s): and    -   e) one or more amine curing agent(s),        wherein the viscosity of said curable composition is no more        than 5 Poise at a temperature within the temperature range of        from about 80° C. to about 130° C.

In the curable composition of the second aspect of the disclosure, thethermoplastic polymer and the epoxy resin component preferably form acontinuous phase.

Preferably, the viscosity of the curable composition is no more thanabout 2 Poise, preferably no more than about 0.5 Poise, and preferablyno more than about 0.2 Poise, and typically at least about 0.1 Poise, ata temperature within the temperature range of from about 80° C. to about130° C. (and preferably at all temperatures within said range).Preferably, the viscosity of the curable composition is no more than 5Poise, preferably no more than about 2 Poise, preferably no more thanabout 0.5 Poise, and preferably no more than about 0.2 Poise, andtypically at least about 0.1 Poise, at a temperature of 120° C.

It will be appreciated that these viscosity values for the curablecomposition when used in a liquid resin infusion process according tothe first aspect of the disclosure refer to the initial viscosity of thecomposition, i,e. at the start of the cure cycle. After approximately 3hours at a temperature within the temperature range of from about 80° C.to about 130° C. (preferably at all temperatures within said range, andpreferably at a temperature of 120° C.), the viscosity of the curablecomposition is preferably no more than 5 Poise, preferably no more than2 Poise, preferably no more than 1 Poise, preferably no more than 0.5Poise, and typically at least 0.3 Poise, more typically at least about0.4 Poise. Thus, it is preferred that not only should the initialviscosity be low but also that the viscosity be stable over time at anelevated processing temperature, in order to ensure that the pot-lifemaintained. As used herein, the term “elevated processing temperature”means above ambient temperature, and encompasses the temperature rangeof from about 80° C. to about 130° C.

According to a third aspect of the present disclosure, there is provideda cured molded article derived from the curable composition definedherein. Preferably, the molded article is a composite material furthercomprising reinforcing fibrous material.

Upon curing, the thermoplastic polymer typically phase-separates fromthe epoxy resin component into aggregate domains, each aggregate domainhaving an “island-like” morphology in a “sea” of epoxy resin. Themorphology of the cured material evolves during the cure cycle. Suchislands-in-the-sea morphology for cured thermoplastic-containing epoxyresin materials are well-known in the art. However, it has now beenfound that the curable compositions of the present disclosure generate anovel morphology by self-assembly of the combination of the inorganicparticles and thermoplastic polymer during the cure of the epoxy resin.According to the present disclosure, the cured composition exhibits aself-assembled shelled morphology of inorganic particles aroundphase-separated thermoplastic polymer domains. In other words, the curedcomposition exhibits a self-assembled shelled morphology of inorganicparticles around, but not within, phase-separated thermoplastic polymerdomains. Thus, the cured composition exhibits a self-assembled shelledmorphology of closely associated inorganic particles around, but notwithin, phase-separated thermoplastic polymer domains. In particular, aproportion of the inorganic particles are disposed around the peripheryof the phase-separated (i.e. aggregate) domains of thermoplastic polymersuch that said inorganic particles substantially surround said domainand form an inorganic rich zone. In cross-section, the inorganicparticles of the self-assembled shelled morphology exhibit a ring-likestructure which substantially surrounds the thermoplastic polymer domainand is reminiscent of a generic core-shell particle morphology. As usedherein, the term “substantially surround” is not intended to infer acontinuous coating of the thermoplastic polymer domain by the inorganicparticles, but instead refers to semi-continuous or discontinuousarrangement of the inorganic particles around the domain, preferablysuch that at least 50%, preferably at least 60%, preferably at least70%, preferably at least 80%, preferably at least 90%, preferably atleast 95% of the outer surface of the thermoplastic polymer domain isproximate to one or more inorganic particle(s). As used herein, the term“proximate” means that any point on the outer surface of thethermoplastic polymer domain is within 100 nm, preferably within 50 nmof one or more inorganic particle(s). The skilled person will appreciatethat the term “phase-separated thermoplastic polymer domains” refers tothe islands-in-the-sea morphology of cured thermoplastic-containingepoxy resin materials.

Thus, in the molded articles of the present disclosure, the inorganicparticles are not distributed uniformly throughout the cured resin. Incontrast, the core-shell particles are distributed substantiallyuniformly throughout the cured resin in the molded articles of thepresent disclosure.

In the molded articles (particularly the composite materials) of thepresent disclosure, said self-assembled shelled morphology of inorganicparticles around a phase-separated thermoplastic polymer domain hasdimensions quantifiable in three orthogonal directions such that itsdimension in at least one direction is greater than 1000 nm, andpreferably its dimensions in at least two directions are greater than1000 nm, and preferably its dimensions in all three directions aregreater than 1000 nm. The dimensions may be assessed by any suitabletechnique familiar to those skilled in the art, for instancetransmission electron microscopy (TEM). The self-assembled shelledmorphology of inorganic particles around a phase-separated thermoplasticpolymer domain is not present in or introduced into the curablecomposition as a preformed entity, because of the size-limiting andfiltering effect of the preform used in LRI processes, and is insteadself-assembled and generated during the curing cycle. In other words,said self-assembled shelled morphology of inorganic particles around aphase-separated thermoplastic polymer domain is generated in situ duringthe curing cycle.

The present inventors have found that the curable compositions of thepresent disclosure exhibit surprisingly improved processability, and thecured resin materials derived from the curable compositions exhibitsurprisingly improved Compression Strength After Impact (CSAI) and atleast retention of hot-wet open-hole compression (H/W-OHC) strength),for instance relative to the materials disclosed in WO-2011/077094-A1.In particular, the introduction of the inorganic particles and the novelself-assembled shelled morphology results in significantly improvedperformance in the CSAI test, with a significant reduction in damagearea and dent depth.

The curable compositions of the present disclosure are of particular usein the liquid resin infusion manufacturing processes.

Thermoplastic Polymer

The thermoplastic polymer functions as a toughening agent in thecompositions described herein.

The curable composition comprises no more than 5.0 wt % of saidthermoplastic polymer by weight of the curable composition, preferablyno more than about 4.0 wt %, preferably no more than about 3.0 wt %,preferably no more than about 2.0 wt %, and preferably at least about0.05 wt %, preferably at least about 0.1 wt %, preferably at least about0.3 wt %, and typically from about 0.3 wt % to about 4.0 wt %, moretypically from about 0.5 wt % to about 4.0 wt %

The thermoplastic polymer preferably exhibits a glass transitiontemperature (Tg) of at least about 150° C., preferably at least about160° C., preferably at least about 170° C., preferably at least about180° C., and suitably at least about 190° C.

The thermoplastic polymer is preferably a thermoplastic aromaticpolymer, preferably selected from polyarylethers, polyarylsulphides andpolyarylsulphones and copolymers thereof, includingpolyarylethersulphones (PES), polyaryletherethersulphones (PEES),polyarylsulphide-sulphones and polyphenylene oxide (PPO). Saidthermoplastic polymers may be used either alone or in combination. Itwill be appreciated that an essential feature of the thermoplasticaromatic polymer is the requirement that an aromatic group lies within,rather than pendant to, the polymer backbone. Aromatic groups which arependant to the polymer backbone may optionally also be present in thethermoplastic aromatic polymer, provided that the polymer backbonecomprises aromatic groups. As discussed further below, the aromaticgroups within the polymer backbone may carry one or reactive pendantand/or end group(s). As used herein, the term “aromatic polymer” is apolymer wherein the mass fraction of aromatic groups that are linkedtogether in the polymer is at least 51%. preferably at least 60%.

The aromatic groups of the thermoplastic aromatic polymer are preferably1,4-phenylene, 1,3-phenylene, 1,4- or 2,6-naphthylene, andphthalimid-N-4-ylene. Of particular utility are phenylene groups,typically 1,4-phenylene.

Preferred thermoplastic aromatic polymers are polyarylether sulphones,for instance poly-1,4-phenylene-oxy-1,4-phenylene-sulphone: thepolyether sulphone made from bisphenol A and dichlorodiphenyl sulphone:and poly-bis(1,4-phenylene)-oxy-1,4-phenylene-sulphone. A furtherpreferred thermoplastic aromatic polymer is poly(p-phenylene sulphide).A further preferred thermoplastic aromatic polymer is poly(p-phenyleneoxide).

The polyarylethersulphone thermoplastic polymer comprises ether-linkedrepeating units, optionally further comprising thioether-linkedrepeating units, the units being selected from:

—[ArSO₂Ar]_(n)—

and optionally from:

—[Ar]_(a)—

wherein:

Ar is phenylene:

n=1 to 2 and can be fractional:

a=1 to 3 and can be fractional and when a exceeds 1, said phenylenegroups are linked linearly through a single chemical bond or a divalentgroup other than —SO₂— (preferably wherein the divalent group is a group—C(R⁹)₂— wherein each R⁹ may be the same or different and selected fromH and C₁₋₈ alkyl (particularly methyl)), or are fused together,

provided that the repeating unit —[ArSO₂Ar]_(n)— is always present inthe polyarylethersulphone in such a proportion that on average at leasttwo of said —[ArSO₂Ar]_(n)— units are in sequence in each polymer chainpresent,

and wherein the polyarylethersulphone has one or more reactive pendantand/or end group(s),

By “fractional” reference is made to the average value for a givenpolymer chain containing units having various values of n or a.

The phenylene groups in the polyarylethersulphones may be linked througha single bond.

The phenylene groups in the polyarylethersulphones may be substituted byone or more substituent groups, each independently selected from C₁₋₈branched or straight chain aliphatic saturated or unsaturated aliphaticgroups or moieties optionally comprising one or more heteroatomsselected from O, S, N, or halo (for example Cl or F); and/or groupsproviding active hydrogen especially OH, NH₂, NHR^(a) or —SH, whereR^(a) is a hydrocarbon group containing up to eight carbon atoms, orproviding other cross-linking activity especially benzoxazine, epoxy,(meth)acrylate, cyanate, isocyanate, acetylene or ethylene, as in vinyl,allyl or maleimide, anhydride, oxazoline and monomers containingunsaturation.

Preferably, the phenylene groups are meta- or para- (preferably para). Amixture of conformations (particularly meta- and para- conformations)may be present along the polymer backbone.

Preferably the polyarylethersulphone comprises a combination of—[ArSO₂Ar]_(n)— and —[Ar]_(a)— repeating units, linked by ether and/orthio-ether linkages, preferably by ether linkages. Thus, preferably thepolyarylethersulphone comprises a combination of polyethersulphone (PES)and polyetherethersulphone (PEES) ether-linked repeating units.

The relative proportions of —[ArSO₂Ar]_(n)— and —[Ar]_(a)— repeatingunits is such that on average at least two —[ArSO₂Ar]_(n)— repeatingunits are in immediate mutual succession in each polymer chain present,and the ratio of —[ArSO₂Ar]_(n)— units to —[Ar]_(a)— units is preferablyin the range 1:99 to 99:1, more preferably 10:90 to 90:10. Typically,the ratio [ArSO₂Ar]_(n):[Ar]_(a) is in the range 75:25 to 50:50.

The preferred repeating units in the polyarylethersulphones are:

—X—Ar—SO₂—Ar—X—Ar—SO₂—Ar— (referred to herein as a “PES unit”)   (I):

and

—X—(Ar)_(a)—X—Ar—SO₂—Ar— (referred to herein as a “PEES unit”)   (II):

wherein:)

X is O or S (preferably O) and may differ from unit to unit; and

the ratio of units I:II is preferably in the range of from 10:90 to80:20, more preferably in the range of from 10:90 to 55:45, morepreferably in the range of from 25:75 to 50:50, and preferably the ratioI:II is in the range of from 20:80 to 70:30, more preferably in therange of from 30:70 to 70:30, most preferably in the range of from 35:65to 65:35.

The preferred relative proportions of the repeating units of thepolyarylethersulphone may be expressed in terms of the weight percentSO₂ content, defined as 100 times (weight of SO₂)/(weight of averagerepeat unit). The preferred SO₂ content is at least 22, preferably 23 to25%, When a=1 this corresponds to PES/PEES ratio of at least 20:80,preferably in the range 35:65 to 65:35.

The flow temperature of polyetherethersulphone is generally less thanthat of a corresponding Mn polyethersulphone, but both possess similarmechanical properties. Accordingly the ratio may be determined, bydetermining values for a and n above.

U.S. Pat. No. 6,437,080, discloses processes for obtaining suchcompositions from their monomer precursors in a manner to isolate themonomer precursors in selected molecular weight as desired.

The above proportions refer only to the units mentioned. In addition tosuch units the polyarylethersulphone may contain up to 50% molar,preferably up to 25% molar, of other repeating units; the preferred SO₂content ranges then apply to the whole polymer. Such units may be forexample of the formula:

in which L is a direct link, oxygen, sulphur, —CO— or a divalent group(preferably a divalent hydrocarbon radical, preferably wherein thedivalent group is a group —C(R¹²)₂— wherein each R¹² may be the same ordifferent and selected from H and C₁₋₈ alkyl (particularly methyl)).

When the polyarylethersulphone is the product of nucleophilic synthesis,its units may have been derived for example from one or more bisphenolsand/or corresponding bis-thiols or phenol-thiols selected fromhydroquinone, 4,4′-dihydroxybiphenyl, resorcinol, dihydroxynaphthalene(2,6 and other isomers), 4,4′-dihydroxybenzophenone,2,2′-di(4-hydroxyphenyl)propane and -methane. If a bis-thiol is used, itmay be formed in situ, that is, a dihalide may be reacted with an alkalisulphide or polysulphide or thiosulphate.

Other examples of such additional units are of the formula:

in which Q and Q′, which may be the same or different, are CO or SO₂;Ar′ is a divalent aromatic radical; and p is 0, 1, 2, or 3, providedthat p is not zero where Q is SO_(2.) Ar′ is preferably at least onedivalent aromatic radical selected from phenylene, biphenylene orterphenylene. Particular units have the formula:

where q is 1, 2 or 3. When the polymer is the product of nucleophilicsynthesis, such units may have been derived from one or more dihalides,for example selected from 4,4′-dihalobenzophenone,4,4′bis(4-chlorophenylsulphonyl)biphenyl, 1,4,bis(4-halobenzoyl)benzeneand 4,4′-bis(4-halobenzoyl)biphenyl. They may of course have beenderived partly from the corresponding bisphenols.

The polyarylethersulphone may be the product of nucleophilic synthesisfrom halophenols and/or halothiophenols. In any nucleophilic synthesisthe halogen if chlorine or bromine may be activated by the presence of acopper catalyst. Such activation is often unnecessary if the halogen isactivated by an electron withdrawing group. In any event, fluoride isusually more active than chloride. Any nucleophilic synthesis of thepolyarylethersulphone is carried out preferably in the presence of oneor more alkali metal salts, such as KOH, NaOH or K₂CO₃ in up to 10%molar excess over the stoichiometric.

As noted above, the polyarylethersulphone contains one or more reactivependant and/or end-group(s), and in a preferred embodiment thepolyarylethersulphone contains two such reactive pendant and/orend-group(s). Alternatively, the polyarylethersulphone comprises onesuch reactive pendant- and/or end-group. Preferably, the reactivependant- and/or end-groups are groups providing active hydrogen,particularly OH, NH₂, NHR^(b) or —SH (where R^(b) is a hydrocarbon groupcontaining up to eight carbon atoms), or are groups providing othercross-linking activity, particularly benzoxazine, epoxy, (meth)acrylate,cyanate, isocyanate, acetylene or ethylene, as in vinyl, allyl ormaleimide, anhydride, oxazaline and monomers containing saturation. Inone embodiment, the reactive pendant- and/or end-groups are of formula—A′-Y wherein A′ is a bond or a divalent hydrocarbon group, preferablyaromatic, preferably phenyl. Examples of Y are groups providing activehydrogen, particularly OH, NH₂, NHR^(b) or —SH (where R^(b) is ahydrocarbon group containing up to eight carbon atoms), or groupsproviding other cross-linking activity, particularly benzoxazine, epoxy,(meth)acrylate, cyanate, isocyanate, acetylene or ethylene, as in vinyl,allyl or maleimide, anhydride, oxazaline and monomers containingsaturation. The groups providing other cross-linking activity may bebound to the Ar groups of the polyarylethersulphone via a direct bond,or via an ether, thioether, sulphone, —CO— or divalent hydrocarbonradical linkage as described hereinabove, most typically via an ether,thioether or sulphone linkage. In a further embodiment, the end-groups,but preferably no more than a relatively minor proportion thereof, maybe selected from halo groups (particularly chloro). Reactive end-groupsmay be obtained by a reaction of monomers or by subsequent conversion ofproduct polymers prior to, or subsequently to, isolation. In one methodfor the introduction of reactive pendant and/or end-groups, for instanceusing activated aromatic halogenides (eg. dichlorodiphenylsulphone) asthe starting material for the polymer, the synthetic process utilises aslightly more than stoichiometric amount of the activated aromatichalogenide, and the resulting polymer having terminal halogenate groupsis then reacted with an aminophenol (e.g. m-aminophenol) to create aminoend groups.

The reactive pendant- and/or end-group(s) is/are preferably selectedfrom groups providing active hydrogen, particularly OH and NH₂,particularly NH₂. Preferably, the polymer comprises two such groups.

The number average molar mass M_(n) of the polyarylethersulphone issuitably in the range from about 2,000 to about 30,000, preferably fromabout 2,000 to about 25,000, preferably from about 2,000 to about15,000, and suitably from about 3,000 to about 10,000 g/mol.

The synthesis of the polya lethersulphone is further described in US2004/0044141 and U.S. Pat. No. 6,437,080.

Resin and Curing Agent

The curable composition comprises an epoxy resin component of one ormore epoxy resin precursor(s). The epoxy resin component is athermosetting epoxy resin component. The epoxy resin precursorpreferably has at least two epoxide groups per molecule, and may be apolyfunctional epoxide having three, four, or more epoxide groups permolecule. The epoxy resin precursor is suitably liquid at ambienttemperature. Suitable epoxy resin precursors include the mono- orpoly-glycidyl derivative of one or more of the group of compoundsconsisting of aromatic diamines, aromatic monoprimary amines,aminophenols, polyhydric phenols, polyhydric alcohols, polycarboxylicacids and the like, or a mixture thereof.

Preferred epoxy resin precursors are selected from:

(i) glycidyl ethers of bisphenol A, bisphenol F, dihydroxydiphenylsulphone, dihydroxybenzophenone, and dihydroxy diphenyl;

(ii) epoxy resins based on Novolacs; and

(iii) glycidyl functional reaction products of m- or p-aminophenol, m-or p-phenylene diamine, 2,4-, 2,6- or 3,4-toluylene diamine, 3,3′- or4,4′-diaminodiphenyl methane, particularly wherein the epoxy resinprecursor has at least two epoxide groups per molecule.

Particularly preferred epoxy resin precursors are selected from thediglycidyl ether of bisphenol A (DGEBA); the diglycidyl ether ofbisphenol F (DGEBF): O,N,N-triglycidyl-para-aminophenol (TG PAP);O,N,N-triglycidyl-meta-aminophenol (TGMAP); andN,N,N′,N′-tetraglycidyldiaminodiphenyl methane (TGDDM). For instance,the epoxy resin precursors may be selected from DGEBA and DGEBF andblends thereof. In a preferred embodiment, epoxy resin precursors areselected from DGEBF and TGPAP and blends thereof.

The epoxy group to amino hydrogen equivalent ratio is preferably in therange from 1.0 to 2.0. Formulations displaying an excess of epoxy arepreferred to the exact stoichiometry.

Commercially available epoxy resin precursors suitable for use in thepresent disclosure include N,N,N′,N′-tetraglycidyl diaminodiphenylmethane (e.g. grades MY 9663, MY 720 or MY 721; Huntsman);N,N,N′,N′-tetraglycidyl-bis(4-aminophenyl)-1,4-diiso-propylbenzene (e.g,EPON 1071; Momentive);N,N,N′,N′-tetraclycidyl-bis(4-amino-3,5-dimethylphenyI)-1,4-diisopropylbenzene,(e.g, EPON 1072; Momentive); triglycidyl ethers of p-aminophenol (e.g.MY 0510; Hunstman); triglycidyl ethers of m-aminophenol (e.g. MY 0610;Hunstman); diglycidyl ethers of bisphenol A based materials such as2,2-bis(4,4′-dihydroxy phenyl) propane (e,g. DER 661 (Dow), or EPON 828(Momentive) and Novolac resins preferably of viscosity 8-20 Pa s at 25°C.: glycidyl ethers of phenol Novolac resins (e,g. DEN 431 or DEN 438;Dow); di-cyclopentadiene-based phenolic Novolac (e.g. Tactix 556,Huntsman); diglycidyl 1,2-phthalate (e.g. GLY CEL A-100); diglycidylderivative of dihydroxy diphenyl methane (Bisphenol F) (e.g. PY 306;Huntsman). Other epoxy resin precursors include cycloaliphatics such as3′,4′-epoxycyclohexyl-3,4-epoxycyclohexane carboxylate (e.g. CY 179;Huntsman).

Preferably, the epoxy resin component is a blend of epoxy resinprecursors having the same or different functionality (wherein the term“functionality” in this context means the number of functional epoxidegroups). The blend of epoxy resin precursors may comprise one or moreepoxy resin precursors having two epoxide groups per molecule(hereinafter referred to as precursor(s) P2), and/or one or more epoxyresin precursors having three epoxide groups per molecule (hereinafterreferred to as precursor(s) P3), and/or one or more epoxy resinprecursors having four epoxide groups per molecule (hereinafter referredto as precursor(s) P4). The blend may also comprise one or more epoxyresin precursors having more than four epoxide groups per molecule(hereinafter referred to as precursor(s) PP). For instance, only P3precursor(s) are present. Alternatively, only P4 precursor(s) arepresent. Suitably, a blend of epoxy resin precursors comprises:

(i) from about 0 wt % to about 60 wt % of epoxy resin precursor(s) (P2);

(ii) from about 0 wt % to about 55 wt % of epoxy resin precursor(s)(P3); and

(iii) from about 0 wt % to about 80 wt % of epoxy resin precursor(s)(P4).

In one embodiment, the blend comprises only one epoxy resin precursor ofa given functionality, in the proportions noted above.

The curable compositions of the disclosure are thermally curable.

The composition comprises one or more amine curing agent(s). Such curingagents are known in the art, and include compounds having a molecularweight up to 500 per amino group, for example an aromatic amine or aguanidine derivative. An aromatic amine curing agent is preferred,preferably an aromatic amine having at least two amino groups permolecule. Examples include diaminediphenyl sulphones, for instance wherethe amino groups are in the meta- or in the para-positions with respectto the sulphone group. Particular examples of amine curing agentssuitable for use in the present disclosure are 3,3′- and4-,4′-diaminodiphenylsulphone (DDS); 4,4′-methylenedianiline (MDR);bis(4-amino-3,5-dimethylphenyl)-1,4-diisopropylbenzene;bis(4-aminophenyl)-1,4-diisopropylbenzene;4,4′-methylenebis-(2,6-diethyl)-aniline (MDEA: Lonza):4,4′-methylenebis-(3-chloro,2,6-diethyl)-aniline (MCDEA; Lonza);4,4′methylenebis-(2,6-diisopropyl)-aniline (M-DIPA; Lonza); 3,5-diethyltoluene-2,4/2,6-diamine (D-ETDA 80: Lonza);4,4′methylenebis-(2-isopropyl-6-methyl)-aniline (M-MIPA; Lonza);4-chlorophenyl-N,N-dimethyl-urea (e.g. Monuron);3,4-dichlorophenyl-N,N-dimethyl-urea (e.g. Diuron™); dicyanodiamide(Amicure™ CG 1200; Pacific Anchor Chemical); and 9,9bis(aminophenyl)fluorenes such as 9,9bis(3-chloro-4-aminophenyl)fluorene (CAF),9,9-bis(3-methyl-4-aminophenyl)fluorene (OTBAF) and9,9-bis(4-aminophenyl)fluorene. Preferably, the curing agents areselected from MCDEA, MDEA, MDA, 3,3′-DDS and 4,4-DDS, and preferablyfrom MCDEA. MDEA and MDA.

The epoxy resin component and the amine curing agent are preferablypresent in the composition in amounts sufficient to provide a molarratio of amine groups present in the curing agent:epoxy groups presentin the epoxy component of from about 0.5;1.0 to about 1.0:0.5,preferably from about 075:1 to about 1;0.75, preferably from about0.9:1.0 to about 1.0:0.9, typically the ratio is about 1:1.

The epoxy resin component and the curing agent(s) make up the bulk ofthe curable composition, and preferably make up the balance of thecurable composition comprising the thermoplastic polymer, core-shellparticles and inorganic particles. Preferably, the curable compositioncomprises at least about 40 wt %, preferably at least about 45 wt %,preferably no more than about 60 wt %, and preferably no more than about55 wt %, and typically no more than about 50 wt % of the epoxy resincomponent, by weight of the curable composition. Preferably, the curablecomposition comprises at least about 30 wt %, preferably at least about35 wt %, typically at least about 40wt %, preferably no more than about60wt %, preferably no more than about 55 wt %, and typically no morethan about 50 wt % of said one or more amine curing agent(s), by weightof the curable composition.

Core-Shell Particles

The curable composition comprises a plurality of core-shell particles,which function as toughening agents, Core-shell particles comprise aninner core portion and an outer shell portion which substantiallyencases the inner core portion. The core portion is preferably apolymeric material having an elastomeric or rubber property, i.e. arelatively low glass transition temperature (particularly relative tothe material of the outer shell portion) and preferably less than about0° C, e,g. less than about −30° C. The outer shell portion is preferablya glassy polymeric material, i.e. a thermoplastic or cross-linkedthermoset polymer having a glass transition temperature greater thanambient temperature (20° C.), preferably greater than about 50° C.

The core portion may comprise a silicone rubber. The core monomers arepreferably selected from isoprene, butadiene, styrene and siloxane. Thepolymeric material of the core portion may be selected from homopolymersof isoprene or butadiene. Copolymers of isoprene or butadiene with up toabout 30 mol % (typically no more than 20 mol %, typically no more than10 mol %) of a vinyl comonomer may also be used, particularly whereinthe vinyl monomer is selected from styrene, alkylstyrene, acrylonitrileand an alkyl methacrylate (particularly butyl methacrylate). Preferablythe core material is selected from polybutadiene-styrene copolymers andpolybutadiene, and blends thereof. Preferably the polybutadiene-styrenecopolymer comprising up to about 30 mol % (typically no more than 20 mol%, typically no more than 10 mol %) of styrene.

The polymeric material of the outer shell is preferably selected fromhomopolymers of styrene, alkylstyrene and alkylmethacrylate (preferablymethyl methacrylate), and copolymers comprising at least 70 mol % of amonomer selected from styrene, alkylstyrene and alkylmethacrylate(preferably methylmethacrylate) and further comprising at least onecomonomer selected from said other comonomers, vinyl acetate andacrylonitrile. The polymeric material of the outer shell may befunctionalized by introducing therein (e.g. by grafting or as acomonomer during polymerisation) unsaturated functional monomers such asunsaturated carboxylic acid anhydrides, unsaturated carboxylic acids andunsaturated epoxides (for instance, maleic anhydride, (meth)acrylic acidand glycidyl methacrylate. The polymeric material of the outer shell maybe cross-linked and optionally further comprises one or morecross-linkable monomer(s), as are known in the art, such asmethacrylamide (MA), acrylamide, N-methylol methacrylamide andN-methylol acrylamide. A preferred polymeric material of the outer shellis a homopolymer or copolymer of methylmethacrylate, optionallyfunctionalised and/or cross-linked, as described above.

A preferred core-shell particle comprises a core material ofpolybutadiene-styrene copolymer, and an outer shell which is ahomopolymer or copolymer of methylmethacrylate optionally functionalisedand/or cross-linked, as described above.

The core portion of the core-shell particle advantageously makes up fromabout 70 to 90 wt % of the core-shell particle and the shell portionfrom about 10 to about 30 wt %.

Commercially available core-shell particles suitable for use in thepresent disclosure include MX660 and MX411, manufactured by Kaneka,Corp.

The curable composition comprises no more than 5.0 wt %, preferably nomore than about 4.0 wt %, preferably no more than about 3.0 wt %,preferably no more than about 2.0 wt %, preferably at least about 0.05wt %, preferably at least about 0.1 wt %, preferably at least about 0.5wt %, and typically from about 0.3 wt % to about 4.0 wt %, of core-shellparticles by weight of the curable composition.

The core-shell particles have a particle size in the range of from about50 nm to about 800 nm, preferably in the range of from about 100 nm toabout 200 nm.

The core-shell particles may be in the form of a dry powder.Alternatively, the core-shell particles may be in the form of acomposition (typically a concentrate or masterbatch) comprising thecore-shell particles and a carrier component, preferably wherein thecarrier component is selected from a thermoplastic polymer or an epoxyresin component as described herein, and preferably wherein the carriercomponent is the same as a thermoplastic polymer or an epoxy resincomponent already present in the curable composition as component (a) or(d).

Inorganic Particles

The curable composition comprises no more than 5.0 wt %, preferably nomore than about 4.0 wt %, preferably no more than about 3.0 wt %,preferably no more than about 2.0 wt %, preferably at least about 0.05wt %, preferably at least about 0.1 wt %, preferably at least about 1.0wt %, and typically in the range of from about 0.1 to about 4.0 wt %, ofinorganic particles by weight of the curable composition.

The inorganic particles have a particle size in the range of from about2.0 nm to about 800 nm, and preferably at least about 10 nm, preferablyno more than 500 nm, preferably no more than 200 nm, preferably no morethan 100 nm. and typically no more than about 50 nm.

The inorganic particles may be in the form of a dry powder.Alternatively, the inorganic particles may be in the form of acomposition (typically a concentrate or masterbatch) comprising theinorganic particles and a carrier component, preferably wherein thecarrier component is selected from a thermoplastic polymer or an epoxyresin component as described herein, and preferably wherein the carriercomponent is the same as a thermoplastic polymer or an epoxy resincomponent already present in the curable composition as component (a) or(d). Any carrier component present in a composition comprising theinorganic particles may be the same as or different to any carriercomponent present in a composition comprising the core-shell particles.

The inorganic particles are preferably selected from particles of metalsalts (for instance calcium carbonate) and metal oxides, more preferablyfrom metal oxides and preferably from SiO₂. TiO₂ and Al₂O₃, and mostpreferably from silica. The particles may be referred to asnano-particles.

The inorganic particles may be selected from any suitable grade of suchparticles known and conventional in the art. For instance, severalgrades of nano-silica are commercially available. The nano-silicaparticles are preferably substantially spherical. The nano-silicaparticles may be chemically synthesised from aqueous sodium silicatesolution.

Applications of the curable polymer compositions and cured thermosetresin compositions

The curable compositions described herein are suitable for fabricationof molded structural materials, and particularly suitable forfabrication of structures, including load-bearing or impact-resistingstructures. The compositions may be used neat, but are typically areused to prepare composite materials further comprising reinforcingfibrous material.

The fiber reinforcement, fabric or pre-shaped fibrous reinforcement (orpreform) may comprise any suitable reinforcing fibrous materialconventional in the art. Fibres can be short or chopped, typically ofmean fibre length not more than 2 cm, for example about 6 mm.Alternatively, and preferably, the fibres are continuous. Combinationsof both short and/or chopped fibres and continuous fibres may also beutilised. The fibres may be in the form of, for example,uni-directionally disposed fibres, woven fabrics or braided, knitted(including multi-warp knitted fabrics and fully-fashioned knit fabrics),non-crimp fabrics, non-woven fabrics, or tapes. The fibrous material maybe in the form of a preform. Fibres are typically used at aconcentration of least 20%, especially from 30% to 70%, more especially50 to 70% by volume, relative to the total volume of the compositioncomprising the resin system and reinforcing agent(s). The fibre can beorganic, especially of stiff polymers such as poly paraphenyleneterephthalamide, or inorganic, Among inorganic fibres, glass fibres suchas “E” or “S” can be used, or alumina, zirconia, silicon carbide, othercompound ceramics or metals. A very suitable reinforcing fibre iscarbon, especially as graphite. The fibre is preferably unsized or issized with a material that is compatible with the resin systems, in thesense of being soluble in the liquid precursor composition withoutadverse reaction or of bonding both to the fibre and to thethermoset/thermoplastic components.

Thus, as described above, the present disclosure provides a moldedarticle comprising, or derived from, the curable composition definedherein. Preferably, the molded article is a composite materialcomprising, or derived from, the curable composition defined herein, andfurther comprising reinforcing fibrous material.

The curable compositions of the present disclosure find particularutility in the manufacture of components suitable for use in transportapplications (including aerospace, aeronautical, nautical and landvehicles, and including the automotive, rail and coach industries), inbuilding/construction applications or in other commercial applications.In the aerospace and aeronautical industry, the compositions may be usedto manufacture primary and secondary parts of the aircraft, andparticularly for primary parts (for example wing, fuselage, pressurebulkhead etc.).

Thus, the present disclosure provides a process for producing such amolded article or a cured thermoset resin from the curable compositionaccording to the second aspect of the disclosure defined herein,comprising the steps of providing said curable composition and curingsaid curable composition.

The provision of the curable composition generally comprises an initialstep of mixing the resin precursor component(s) with the tougheningagents, optionally followed by a cooling step. Where the curablecomposition comprises a plurality of resin precursor components, two ormore of said plurality of resin precursor components are typicallypre-mixed prior to the addition of the toughening agents, and typicallysaid pre-mixing is followed by a heating step (suitably at a temperaturefrom above room temperature to about 80° C.) prior to the addition ofthe toughening agents. The toughening agents are preferably introducedby adding the thermoplastic component first, followed by the core-shellparticles and the inorganic particles. Addition of the thermoplasticcomponent is typically effected at above room temperature (suitably at atemperature of up to about 120° C.) until the thermoplastic hasdissolved. After an optional cooling step (typically such that themixture is at a temperature in the range of from about 70 to about 90°C.), the core-shell and inorganic particles are added, sequentially orsimultaneously. It will be appreciated that the introduction of eachadditional component is accompanied by stirring or other mixingtechnique. The core-shell particles are preferably added as amasterbatch in a resin precursor component. Similarly, the inorganicparticles are preferably added as a masterbatch in a resin precursorcomponent. The resin precursor component of a masterbatch comprising thecore-shell particles may be the same as or different to the resinprecursor component of a masterbatch comprising the inorganic particles.A masterbatch may comprise one or more resin precursor component(s) andpreferably comprises only a single resin precursor component.Alternatively, the core-shell particles and/or the inorganic particlesmay be added to the composition as a dry powder. In a furtheralternative, the core-shell particles and/or the inorganic particles maybe compounded with the thermoplastic component prior to its mixing withthe resin precursor component(s). Where the curable compositioncomprises a plurality of resin precursor components, one or more of theresin precursor components may be added into the composition at anystage during the preparation of the curable composition; thus forinstance, where the curable composition comprises at least 3 (forinstance 3 or 4) resin precursor components, then a plurality of saidresin precursor components are preferably premixed as describedhereinabove, and at least one (and typically only one) of the resinprecursor components are introduced subsequently, for instance after theaddition of at least one of said toughening agent(s), and particularlyafter the addition of all of said toughening agents. The curing agent(s)are then added, and the mixture is stirred until the curing agent hasfully dissolved.

The curable composition is then injected into a mold, typically in whichhas been disposed reinforcing fibrous material, and the curablecomposition then cured at an elevated temperature to form the curedmolded article.

Thus, the present disclosure preferably provides a liquid resin infusion(LRI) manufacturing process, preferably Resin Transfer Molding (RTM),more preferably Vacuum-Assisted Resin Transfer Molding (VARTM),comprising the steps of:

(i) preparing a preform comprising reinforcing fibrous material;

(ii) laying the preform within a mold;

(iii) heating the mold to a predetermined temperature;

(iv) providing a curable composition as defined herein;

(v) injecting the curable composition into the mold, and

(vi) curing said curable composition.

The process may be also be a liquid resin infusion process which isselected from the processes referred to in the art as Resin Infusionwith Flexible Tooling (RIFT), Constant Pressure Infusion (CPI), BulkResin Infusion (BRI), Controlled Atmospheric Pressure Resin Infusion(CAPRI), Seemann Composites Resin Infusion Molding Process (SCRIMP),Vacuum-assisted Resin Infusion (VARI) or Resin Transfer Injection (RTI)used to manufacture composite articles.

The preform may comprise one or more layers of fabric comprisingreinforcing fibrous material, as described herein.

The predetermined temperature of the mold is typically in the range offrom about 90° C. to about 120° C., typically from about 100° C. to 110°C.

Curing is suitably carried out at elevated temperature using a curetemperature (T_(C)) of up to 200° C., preferably at least 140° C.,preferably at least 160° C., preferably in the range from 160 to 195°C., more preferably from 170 to 190° C., and more preferably from 175 to185° C. The cure temperature (T_(C)) is attained by heating at a cureramp rate (R_(CR)) which is preferably at least about 0.05° C./min,preferably at least about 0.1° C./min, preferably at least about 0.5°C./min, and typically up to about 5.0° C./min, typically up to about3.0° C./min, more typically up to about 2.5° C./min, and preferably inthe range of from about 0.5° C./min to about 2.5° C./min. The curetemperature is maintained for the required period, which is typically atleast about 60 minutes and typically no more than about 500 minutes, andpreferably at least about 90 minutes and preferably no more than about180 minutes, and typically about 120 minutes. Typically, the cured resinis cooled, typically to ambient temperature, at a controlled rate(preferably in the range of from about 0.5° C./min to about 2.5° C./min,and typically at a rate of 2° C./min).

The preform may be sealed in the mold by at least a vacuum bag.

For improved processability of the curable composition, for instancewherein the composition exhibits the preferred viscosity characteristicsdescribed herein, it is preferred that the curable compositioncomprises:

(i) no more than about 3.0 wt %, preferably no more than about 2.0 wt %of said thermoplastic polymer by weight of the curable composition;and/or

(ii) no more than about 3,0 wt %, preferably no more than about 2.0 wt %of core-shell particles by weight of the curable composition; and/or

(iii) no more than 3.0 wt %, preferably no more than about 2.0 wt %, ofi organic particles by weight of the curable composition,

preferably wherein the curable composition satisfies at least criterion(i) above, and preferably wherein the curable composition satisfies atleast two of criteria (i) to (iii) above (and preferably at leastcriterion (i)), and preferably all three of criteria (i) to (iii) aboveare satisfied.

According to a fourth aspect of the disclosure, there is provided theuse of the curable composition defined herein in an LRI process, for thepurpose of improving CSAI in a cured resin (particularly a compositematerial) produced from said curable composition in said LRI process,particularly for the purpose of improving CSAI without detriment to theprocessability of the curable composition and preferably for the purposeof improving CSAI while simultaneously improving processability of thecurable composition. Preferably said use is for the purpose of improvingCSAI while maintaining excellent compressive performance (particularlyhot-wet open-hole compression (H/W-OHC) strength) in a cured resin(particularly a composite material) produced from said curablecomposition, particularly wherein the processability of said curablecomposition is at least maintained and preferably improved. Preferably,reference to improvement or retention of said properties is to theimprovement or retention of a property relative to a material which doesnot contain the combination of thermoplastic component, core-shellparticles and inorganic particles.

Thus, in the use according to the fourth aspect of the disclosure, theimprovement is such that the CSAI of said cured resin (particularly saidcomposite material) is at least 220, preferably at least 230, and morepreferably at least 240 MPa, preferably wherein the H/W-OHC strength ofsaid cured resin (particularly said composite material) is at least 190,preferably at least 195, preferably at least 200, preferably at least205, preferably at least 210 MPa, and/or preferably wherein the initialviscosity of said curable composition is no more than 5 Poise at atemperature within the temperature range of from about 80° C. to about130° C. (preferably at 120° C.) and the viscosity of said curablecomposition after 3 hours at a temperature within the temperature rangeof from 80° C. to 130° C. (preferably at 120° C.) is no more than 5Poise,

As used herein, the terms “excellent hot-wet compressive performance” or“excellent hot-wet open-hole compression (H/W-OHC) strength” refer to anH/W-OHC strength of at least 190, preferably at least 195, preferably atleast 200, preferably at least 205, preferably at least 210 MPa in thetest method described herein.

Preferably, the molded article (preferably the composite material)defined herein exhibits a CSAI of at least 210, more preferably at least220, more preferably at least 230, and more preferably at least 240 MPain the test method described herein.

The disclosure is now illustrated in non-limiting manner with referenceto the following examples.

Experimental

The physical properties and behaviour of the resin systems describedherein are measured according to the following techniques.

Glass Transition Temperature

The glass transition temperature is defined as the temperature where thesample exhibits a dramatic change in mechanical and damping behaviourwith increasing temperature when subjected to an oscillatingdisplacement. The Tg onset is defined as the temperature intersection ofextrapolated tangents drawn from points on the storage modulus curvebefore and after the onset of the glass transition event. The test wasperformed using TA Q800 in a single cantilever bending mode in the rangeof temperatures between about 50″ C. and 300′ C., with a heating rate of5±0.2° C./min and 1 Hz frequency.

Particle Size

Particle size was measured by dynamic light scattering using a MalvernZetasizer 2000. Reference herein to particle size is to the median (d50)of the particle size distribution, the value on the distribution suchthat 50% of the particles have a particle size of this value or less.The particle size is suitably a volume-based particle sized, i.e.d(v,50)

Viscosity

Dynamic temperature ramp viscosity of the resin formulations wasmeasured according to the method of ASTM D4440. Steady temperatureviscosity of the resin formulations was measured according to the methodof ASTM D4287.

Molar Mass

The molar mass, principally of the thermoplastic component, is measuredby Gel Permeation Chromatography relative to a polystyrene standard.

Mechanical Testing

Mechanical performance was measured in terms of compressive performance(open hole compression (OHC) strength) and impact resistance(compression strength after impact (CSAI).

In order to measure Compression Strength After Impact (CSAI), thecomposite material is subject to an impact of a given energy (30 Jouleimpact) and then loaded in compression in an anti-buckling jig, and theresidual compressive strength measured. Damage area and dent depth aremeasured following the impact and prior to the compression test. Duringthis test, the composite material is constrained to ensure that noelastic instability is taking place and the strength of the compositematerial is recorded. In this work, CSAI (in MPa) was measured accordingto the ASTM D7136-7137 test method.

Open-hole compression strength (in MPa) was measured according to theASTM D6484 test method. OHC measurements were taken at room temperature(approx. 20° C.; RT-OHC). Hot-wet compressive performance (H/W-OHCstrength) was assessed by measuring OHC strength at 160° F. (approx.71.1° C.) after soaking the samples for 14 days in water at 160° F.(approx. 71.1° C.).

Resin systems were prepared and analysed according to the testprocedures described above,

EXAMPLES

A series of resin systems was formulated using the components shown inTable 1 below. Comparative Example 1 is a resin formulation according toWO-2011/077094-A.

TABLE 1 Toughening additives Core- shell rubber PES particles Nano-thermo- Epoxy resin precursors Kaneka silica plastic Cure PY306 MY0510MY0610 MY721 MX411 Nanopox 5003P agent Resin (%) (%) (%) (%) (%) F520(%) (%) MCDEA C. Ex. 1 8.09 16.19 16.19 6.04 2.02 0 3.22 48.24 Ex. 17.41 16.6 16.6 7.03 2.17 0.27 0.51 49.42 (low) Ex. 2 5.25 16.43 16.432.34 6.44 3.73 0.50 48.91 (medium) Ex. 3 0.85 9.10 9.10 0 26.47 9.943.97 40.57 (high)

The following materials were used:

-   -   Araldite® PY306, a diglycidylether of bisphenol F (DGEBF) with a        specific content of epoxide groups of from 5.99 mol/kg to 6.41        mol/kg (an “epoxy equivalent weight” of from 156 g/mol to 167        g/mol) from Huntsman Advanced Materials.    -   Araldite® MY0510, a O,N,N-triglycidyl para-aminophenol (TGPAP)        with a specific content of epoxide groups of from 9.35 mol/kg to        10.53 mol/kg (an “epoxy equivalent weight” of from 95 g/mol to        107 g/mol) from Huntsman Advanced Materials.    -   Araldite® MY721, a N,N,N′,N′-tetraglycidyl        diaminodiphenylmethane (TGDDM) with a specific content of        epoxide groups of from 8.70 mol/kg to 9.17 mol/kg, (an “epoxy        equivalent weight” of from 109 g/mol to 115 g/mol) from Huntsman        Advanced Materials.    -   Araldite® MY0610, a O,N,N-triglycidyl meta-aminophenol (TGMAP)        (epoxy equivalent weight of from 94 g/mol to 102 g/mol) from        Huntsman Advanced Materials.    -   Sumikaexele 5003P a functionalized polyethersulfone (PES)        thermoplastic polymer from Sumitomo.    -   Kaneka® MX411: a masterbatch of core-shell rubber particles        (particle size of 100 nm) (15 wt %) in Araldite® MY721.    -   Nanopox® F520: a masterbatch of nano-silica particles (40 wt %)        in Araldite® PY306.

The compositions were prepared as follows. The PY306, MY0510 and MY0610epoxy precursor components were combined at room temperature and heatedto 60′ C. with stirring. The 5003P PES thermoplastic component was addedand the temperature was raised to 115° C. with further stirring. Whenthe temperature reached 115° C., the mixture was held for 30 minutesuntil the PES thermoplastic has dissolved. The mixture was cooled withstirring to 80′ C., at which point core-shell rubber and nanosilicamasterbatches were added along with the MY721 epoxy precursor component,with further stirring. MCDEA was then added and the mixture was stirreduntil the MCDEA has fully dissolved.

The viscosity of the resin formulations was tested in accordance withthe test method described above, and the results are shown in Table 2below.

Composite materials were then prepared in a VARTM process by injectingeach of the above resin formulations into a mold containing carbon fibrefabric (T300 3k Plain Weave reinforcement (196 gsm) fabric) as follows.80 g of resin was placed into a 6″×4″ mold, warmed to about 90 to 110 °C. and degassed using a vacuum oven. The mold and its contents were thentransferred to a fan oven where they were heated from the startingtemperature (about 90 to 110° C.) up to 180° C. at a rate of 2° C./minand held isothermally for 2 hours before being allowed to cool to roomtemperature at a rate of 2° C./min.

The cured laminates were analysed according to the test methodsdescribed above and the results are shown in Table 2 below,

TABLE 2 C. Ex. 1 Ex. 1 Ex. 2 Ex. 3 RT OHC strength (MPa) 269.2 266.5289.1 253.7 H/W OHC strength (MPa) 206.2 216.9 208.1 197.2 CSAI (MPa)209.9 223.5 242.0 230.4 Dent Depth 1.8 0.41 0.35 0.07 Damaged area 1224922 701 796 Initial viscosity at 120° C. 0.58 0.18 0.17 1.8 (poise)Viscosity at 120° C.; 3 hrs 1.53 0.39 0.42 >3.75* (poise) *Exceeded 4Poise before 3 hr isothermal time completed

The results demonstrate that the improved resin formulations of thepresent disclosure provide composite materials which exhibitsurprisingly improved CSAI. The composites made from the resinformulations of the present disclosure exhibit a smaller damaged areaand lower dent depth. In addition, the composites exhibit excellent FMOHC strength, which is maintained or improved.

Moreover, the resin formulations 1 and 2 exhibit lower viscosity, whichis more stable for longer periods, and hence possess superiorprocessability. The resin formulation of Example 3 exhibits a relativelyhigher viscosity, more akin to that of Comparative Example 1,demonstrating that where improved processability is required in additionto improved CSAI and at least comparable H/W OHC strength, thenformulations closer to Examples 1 or 2 are more desirable. FIG. 3 showsthe viscosity as a function of temperature for the four examples.Examples 1 and 2 exhibit favourable low viscosities even at the lowertemperatures in the range, hence maintaining or extending pot-life.

The resin laminates were analysed by transmission electron microscopy asdescribed above. The morphology of Example 1 is shown in FIG.1, whichshows the self-assembly of inorganic particles (4) around the outersurface of a phase separated thermoplastic domain (2) in the cured resin(1) further comprising core-shell particles (3).

FIG. 2 shows the morphology of a sample similar to Comparative Example1, which contained no nano-silica particles. FIG, 2 shows the phaseseparated thermoplastic domain (2) in the cured resin (1) furthercomprising core-shell particles (3). FIG. 2 shows that removal of thenano-silica from the resin formulation results in the loss of the novelmorphology, and this is accompanied by loss of the improvement in CSAIperformance.

1. A liquid resin infusion (LRI) manufacturing process for producing amolded article, comprising the steps of providing a curable composition,injecting said curable composition into a mold, and curing said curablecomposition, wherein the curable composition comprises: a) no more than5.0 wt % of a thermoplastic polymer: b) no more than 5.0 wt % ofcore-shell particles wherein said core-shell particles have a particlesize in the range of from about 50 nm to about 800 nm: c) no more than5.0 wt % of inorganic particles wherein said inorganic partides have aparticle size in the range of from about 2.0 nm to about 800 nm; d) anepoxy resin component which comprises one or more epoxy resinprecursor(s): and e) one or more amine curing agent(s), wherein theinitial viscosity of said curable composition is no more than 5 Poise ata temperature within the temperature range of from about 80′ C. to about130° C.
 2. A process according to claim 1 wherein the thermoplasticpolymer and the epoxy resin component form a continuous phase in thecurable composition.
 3. A process according to claim 1, wherein saidmolded article exhibits a self-assembled shelled morphology of inorganicparticles around phase-separated thermoplastic polymer domains, whereinsaid self-assembled shelled morphology of inorganic particles aroundphase-separated thermoplastic polymer domains is generated in situduring curing.
 4. A process according to claim 1, wherein said viscosityof the curable composition is no more than 2 Poise, wherein saidviscosity is measured at a temperature of 120° C.
 5. A process accordingto claim 1, wherein the viscosity of said curable composition after 3hours at a temperature within the temperature range of from 80′ C. to130° C. is no more than 5 Poise.
 6. A process according to claim 1,wherein the molded article is a composite material comprisingreinforcing fibrous material.
 7. A process according to claim 1 furthercomprising: (i) preparing a preform comprising reinforcing fibrousmaterial; (ii) laying the preform within a mold; (iii) optionally(heating the mold to a predetermined temperature; (iv) providing saidcurable composition; (v) injecting the curable composition into themold, and (vi) curing said curable composition.
 8. A process accordingto claim 7, wherein the preform comprises one or more layers of fabriccomprising reinforcing fibrous material.
 9. A process according to claim1, wherein the mold is heated to a predetermined temperature in therange of from about 90° C. to about 120° C.
 10. A process according toclaim 1, wherein curing is performed at a cure temperature (T_(C)) inthe range from about 160° C. to about 200° C.
 11. A process according toclaim 1, wherein the thermoplastic polymer is selected frompolyarylethers, polyarylsulphides and polyarylsulphones and copolymersthereof including polyarylether-sulphones, andpolyarylsulphide-sulphones.
 12. A process according to claim 1, whereinthe thermoplastic polymer is selected from polyarylethersulphonethermoplastic polymers comprising ether-linked repeating units,optionally further comprising thioether-linked repeating units, theunits being selected from:—[ArSO₂Ar]_(n)— and optionally from: wherein: Ar is phenylene: n=1 to 2and can be fractional; a=1 to 3 and can he fractional and when a exceeds1, said phenylene groups are linked linearly through a single chemicalbond or a divalent group other than —SO₂—, preferably wherein thedivalent group is a group —C(R⁹)₂— wherein each R⁹ may be the same ordifferent and selected from H and C₁₋₈ alkyl and preferably selectedfrom methyl, or are fused together, provided that the repeating unit—[ArSO₂Ar]_(n)— is always present in the polyarylethersulphone in such aproportion that on average at least two of said —[ArSO₂Ar]_(n)— unitsare in sequence in each polymer chain present, and wherein thepolyarylethersulphone has one or more reactive pendant and/or endgroup(s).
 13. A process according to claim 1, wherein the resinprecursor component comprises one or more epoxy resin precursor(s)having at least two epoxide groups per molecule.
 14. A process accordingto claim 1, wherein the resin precursor component is a blend of epoxyresin precursors having different functionality, wherein said blendcomprises one or more epoxy resin precursors having two epoxide groupsper molecule, and one or more epoxy resin precursors having three orfour epoxide groups per molecule.
 15. A process according to claim 14,wherein the resin precursor component comprises a blend ofdi-functional, tri-functional and tetra-functional epoxy resinprecursors.
 16. A process according to claim 1.xvhepuinihm resinprecursor component comprises at least one epoxy resin precursorselected from: the diglycidyl ether of bisphenol A (DGEBA); thediglycidyl ether of bisphenol F (DGEBF);O,N,N-triglycidyl-para-aminophenol (TGPAP);O,N,N-triglycidyl-meta-aminophenol (TGMAP); andN,N,N′,N′-tetraglycidyldiaminodiphenyl methane (TGDDM), and blendsthereof.
 17. A process according to claim 1, wherein said amine curingagent(s) are selected from: 4,4′methylenebis-(3-chloro,2,6-diethyl)-aniline (MCDEA): 4,4′methylenebis-(2,6-diethyl)-aniline(MDEA); 4,4′-methylenedianiline (MDAy and 3,3′- and4-,4′-diaminodiphenylsulphone (DDS); and combinations thereof.
 18. Aprocess according to claim 1, wherein the epoxy resin component and theamine curing agent are present in the composition in amounts sufficientto provide a molar ratio of amine groups present in the curing agent toepoxy groups present in the epoxy component of from about 0.75:1 toabout 1:0.75.
 19. A process according to claim 1, wherein the curablecomposition comprises from about 0.5 wt % to about 4.0 wt % of saidthermoplastic polymer.
 20. A process according to claim 1, wherein thecurable composition comprises from about 0.3 wt % to about 4.0 wt %core-shell particles and said core-shell particles have a particle sizein the range of from about 100 nm to about 200 nm.
 21. A processaccording to claim 1, wherein the core-shell particles comprise: aninner core portion which is a polymeric material selected fromhomopolymers of isoprene or butadiene, and from copolymers of isopreneor butadiene with up to about 30 mol % of a vinyl comonomer; and anouter shell portion which is a polymeric material selected fromhomopolymers of styrene, alkylstyrene and methyl methacrylate, and fromcopolymers comprising at least 70 mol % of a monomer selected fromstyrene, alkylstyrene and methylmethacrylate and further comprising atleast one different comonomer selected from styrene, alkylstyrene,methylmethacrylate, vinyl acetate and acrylonitrile, wherein saidpolymeric material of the outer shell portion is optionallyfunctionalized by introducing therein one or more unsaturated functionalmonomers.
 22. A process according to claim 1, wherein said inorganicparticles are selected from calcium carbonate, silica (SiO₂), TiO₂ andAl₂O₃.
 23. A process according to claim 22, wherein said inorganicparticles are silica particles.
 24. A process according to claim 1,wherein the curable composition comprises from about 0.1 wt % to about4.0 wt % inorganic particles and said inorganic particles have aparticle size in the range of from about 2.0 nm to about 100 nm.
 25. Acurable composition comprising: a) no more than 5.0 wt % of athermoplastic polymer: b) no more than 5.0 wt % of core-shell particleswherein said core-shell particles have a particle size in the range offrom about 50 nm to about 800 nm; c) no more than 5.0 wt % of inorganicparticles wherein said inorganic particles have a particle size in therange of from about 2.0 nm to about 800 nm; d) an epoxy resin componentwhich comprises one or more epoxy resin precursor(s): and e) one or moreamine curing agent(s), wherein the viscosity of said curable compositionis no more than 5 Poise at a temperature within the temperature range offrom about 80′ C. to about 130° C.
 26. The curable composition of claim26, wherein the inorganic particles are silica particles.
 27. A curedmolded article derived from injecting the composition of claim 25 into afibrous preform to infuse the preform with the composition, and curingthe infused preform, wherein the cured composition exhibits aself-assembled shelled morphology of inorganic particles aroundphase-separated thermoplastic polymer domains.